Honors College Theses

Publication Date



Art 3D Studio (BFA

Document Type and Release Option

Thesis (open access)

Faculty Mentor

Kimberly Riner


Food-safe ceramic glazes can be altered with additives and become harmful to the user of the ceramic ware. Rutile is a frequently used material added to glazes to create variegation in glazes, but it is commonly known to cause defects in the glaze that can be unsafe for food. This experiment is conducted to determine if rutile can be added to food-safe glazes and still retain their food-safe status. A food-safe glaze is a shiny, thin coating that does not leach chemicals or has an excess of colorants; common food-safe glazes are white liners and clear glazes as they have no additives.

To test that food-safe glazes cannot be food-safe with larger additions of rutile, an experiment testing seven different percentages of rutile in four glazes, on five commonly used clay bodies was conducted. 140 cups and test tiles were glazed in the 140 variations and put through seven separate tests to verify their food-safe status. The results showed that sixty-seven out of the 140 variations are food-safe, the majority, twenty-six of the sixty-seven, from John Britt’s Spearmint glaze; conversely, John Britt’s Licorice only had eight variations that were food-safe, five of which were the control cups with no rutile added.

The results suggest that rutile can be added to ceramic glazes in small amounts, depending on the clay body being used. With these results, rutile is a viable option to add these specific ceramic glazes and still be food-safe.

Thesis Summary

This experiment explored the addition of rutile in food-safe glazes. Four glazes were tested on five common clay bodies, testing seven percentages of rutile, totaling 140 variations. After the visual inspection, one hundred made it to the cutlery marking test. Thirty-one cups did not pass the cutlery marking test, leaving sixty-nine variations for the next tests. Only two cups were eliminated from the glaze leaching test- sixty-seven cups passed all remaining tests and were deemed food safe. Of the food-safe glaze variations, Ron Roy & John Hesselberth’s Ol’ Blue had no variegation with the addition of rutile. Additionally, light rutile appears to be incompatible with John Britt’s Licorice glaze as all but eight variations failed the tests.

The various possibilities of rutile in food-safe glazes were only limitedly studied in this experiment. Variegation comes with a higher probability of issues and defects within the glazes, lending itself to constant testing to determine the food-safe quality of the glaze. Food-safe glazes prevent bacteria, mold, and toxic materials from accumulating on or contaminating the glazes, which can subsequently be consumed. Ceramic glazes are essential in sealing the surface of the clay and are often used to decorate ceramic works. It is important for a potter to find the balance between decoration and food-safe qualities when choosing the glaze for work that is designed to be used for food.